1. Field of the Invention
This invention is concerned with an improvement in or relating to an image reproducing apparatus of the type in which a toner image formed on a charge receptor is transferred and fixed on a transfer member by pressure and heat via an intermediate transfer member.
2. Description of the Prior Art
An image-forming process by a reproducing apparatus such as an electrophotographic reproducing apparatus, for example, comprises the steps of forming an electrostatic latent image corresponding to the image of a document on a charge receptor using an insulating photoconductive material as a photosensitive member by corona discharge and light radiation and developing the latent image into a visible image using a toner developer.
The visible image on the charge receptor or the toner image is transferred onto a transfer member by an electric transfer method such as corona discharge or bias roller or by physical means such as applicaton of pressure or heat. The toner image transferred to the transfer member in the manner described above is fixed on the transfer member by ordinary heating means, completing the image-forming process.
In the image-forming process as described above, an electric method such as a transfer method by corona discharge or a bias roller transfer method is available for transferring the toner image formed on the charge receptor to the transfer member. However, the transfer ratio of this method is significantly affected by the environmental conditions such as the ambient temperature and humidity and turbulence of the transferred image is likely to occur. Accordingly, methods other than the electric method have also been examined and a transfer method by application of pressure is known as one of such methods. According to the disclosure of Japanese Patent Publication No. 41,679/1971 and Japanese Patent Laid-Open No. 78,559/1974, for example, a method and apparatus is known in which the toner image on the photosensitive member is wrapped by an elastic heat-resistant intermediate blanket and is transferred without being permitted to remain on the photosensitive member, thereby ensuring the transfer of the image having good quality.
However, since high speed reproduction is one of the requirements of the times, higher fixing efficiency and a higher fixing speed are also required; hence, various means have been attempted in the reproducing apparatus of the transfer/fixing system by the application of pressure and heat using the intermediate transfer member in order to specifically improve the fixing speed. If the heating temperature of a fixing device is raised in a reproducing apparatus using a belt-like intermediate transfer member so as to enhance the fixing speed, the belt-like intermediate transfer member (hereinafter referred to as the "intermediate transfer belt") is heated especially during repetition of reproduction and the intermediate transfer belt thus heated comes into contact with the charge receptor so that the charge receptor is in turn heated and the properties as the photosensitive member are deteriorated.
As a result of intensive studies, the inventors of the present invention have found that it is possible to escape the heat of the intermediate transfer belt to a support roller and also to an auxiliary pressure contact roller by the construction described below and that better effects can thus be obtained. According to the present invention, the support roller described above is disposed inside the intermediate transfer belt so as to support the latter and the temperature of the support roller, which a heat from said support roller heats and fuses the toner image on the intermediate transfer belt, is not set to a high temperature as in the prior art apparatuses but is set to a low temperature considerably below the fusion temperature of the toner so as to reduce the quantity of heat transfer to the intermediate transfer belt. Furthermore, the surface portion of the support roller after passing through the transfer-fixing portion and the intermediate transfer belt are arranged so as to enlarge the contact area therebetween by use of the auxiliary pressure contact roller described above, thus making it possible to escape the heat of the intermediate transfer belt to the support roller. The auxiliary pressure contact roller is made of a heat absorbing material so that the heat of the intermediate transfer belt can also escape to the auxiliary pressure contact roller, as described above.